1. Field of the Invention
The present invention is directed generally to devices and methods for monitoring patient health, and more particularly, to methods and systems for detecting edema.
2. Description of the Related Art
Monitoring patient parameters is quite common in medical care environments, such as hospitals, doctors' offices, and the like. Further, patient monitoring outside of a clinical setting is increasing because of the rising cost of traditional healthcare. There is a need for devices configured to monitor a patient's health. Devices configured to notify professional healthcare providers when appropriate are particularly desirable.
A “compensated” system is able to function despite any stressors or defects that might be present. Decompensation occurs when the system can no longer compensate for these issues. Decompensation is a general term commonly used in medicine to describe a variety of situations.
Cells are surrounded by an extracellular fluid that includes interstitial fluid, plasma, and transcellular fluid. The interstitial fluid is found in the interstitial spaces, also known as the tissue spaces. Edema is an abnormal accumulation of fluid in the interstitial spaces that causes swelling.
Edema in the feet and legs is often referred to as peripheral edema. Limb volume changes have sufficient specificity and sensitivity to be predictive of impending heart failure decompensation in some forms of heart failure. The physiological conditions that cause an increase in interstitial fluid in the limbs of a heart failure patient may also cause decompensation. Therefore, edema may be predictive of congestive chest conditions that can endanger the patient.
There are several traditional methods of measuring or evaluating edema. The most commonly used method is to press a depression into the skin (e.g., of the lower leg) and assign a grade (e.g., on a 1 to 4 scale) indicating an amount of edema present based on the depth and persistence of the depression. This method provides a coarse but useful measure of edema.
More accurate methods of measuring or evaluating edema include placing the patient's limb in a container of water and measuring an amount of fluid displaced by the patient's limb. By collecting two or more displacement measurements, a change in limb volume, if any, that occurred between measurements can be determined. Unfortunately, this method is wet, cumbersome, and unsuitable for continuous patient monitoring and data collection.
A Leg-O-Meter device may be used to measure edema. The Leg-O-Meter device includes a tape measure positioned at a predetermined height above the floor. The tape measure is used to determine a single distance around a limb. While results obtained by the Leg-O-Meter device are well correlated with those obtained using the more cumbersome fluid displacement method, the Leg-O-Meter device requires a skilled practitioner to operate and the active involvement of the patient.
Electronic measurement devices also exist that are large, expensive, and fixed making them unsuitable for a home environment. Further, such devices typically do not provide methods of communicating with the patient, a caregiver, or a healthcare provider. These devices also do not typically analyze the data collected.
Quantifying and monitoring peripheral edema is important because the onset of edema and/or changes in an amount of edema present can occur many days prior to a considerable decline in patient health. In other words, the onset of edema and/or changes in an amount of edema present may predict (e.g., by several days) a significant decline in a patient's health. This predictive indication may be used in some cases to avoid a significant decline in patient health. For example, such early warning of an impending problem may be used to adjust the patient's diet, salt intake, medications, and the like. Further, consultation with healthcare professionals before the decline occurs may avoid precipitous health declines, such as, but not limited to, decompensated heart failure. Therefore, a need exists for methods and systems that provide substantially continuous monitoring of edema. A need also exists for methods and systems that track a patient's physiological parameters and symptoms for the purposes of detecting trends and/or recognizing impending patient health conditions that may require medical intervention, such as hospitalization.
The present application provides these and other advantages as will be apparent from the following detailed description and accompanying figures.